The present invention relates to a scanner unit mounted in a copying machine, etc., and more particularly to a carriage having a cold-cathode fluorescent lamp as a lamp for illuminating an original.
In general, a copying machine has a scanner unit for reading an image from an original, or an object to be copied. The scanner unit has, at its upper surface, a substantially horizontal original table glass for the mounting of the original.
First and second carriages, which extend along the original table glass from a front side to a rear side of the apparatus, that is, in a main scan direction, are disposed below the original table glass. The first carriage includes a lamp for illuminating the original placed on the original table glass, a reflector for converging light from the lamp onto the surface of the original, and a first mirror for deflecting the reflection light from the original at 90°. The second carriage has second and third mirrors for respectively deflecting the reflection light from the first mirror at 90°. The reflection light from the third mirror is guided to a light receiving element via a converging lens and photoelectrically converted to produce image data.
A plurality of rails extending in a sub-scan direction perpendicular to the main scan direction are provided on the front and rear sides of the scanner unit. Both ends of frames of the first and second carriages are placed on the rails and kept substantially horizontal. Each carriage is thus made slidable in the sub-scan direction along the rails.
Front-side end portions of the first and second carriages are coupled by means of a wire cable passed over a plurality of pulleys, and also rear-side end portions of the carriages are coupled by means of a wire cable passed over a plurality of pulleys. By driving the two wire cables, the first carriage is slid in the sub-scan direction at a constant speed along the rails, and the second carriage is slid in the sub-scan direction along the rails at a ½ speed, following the movement of the first carriage.
Recently, there is a demand for reduction in size of the scanner unit, and accordingly there is a tendency to use an elongated cold-cathode fluorescent lamp having a diameter of about 4 mm as the lamp disposed on the first carriage. The quantity of heat generated by the cold-cathode fluorescent lamp is relatively small, and it can be disposed near the original table glass without heating the original table glass. Since the cold-cathode fluorescent lamp can be disposed very close to the original table glass, the dimension of the scanner unit in the height direction can be reduced.
In addition, an inverter circuit board functioning as a lighting circuit for turning on the cold-cathode fluorescent lamp needs to be mounted on the first carriage. The inverter circuit board is attached to a substantially middle portion of the first carriage in the main scan direction, in consideration of a weight balance of the first carriage in the main scan direction.
The weight balance of the first carriage is important. If the weight balance is lost, a greater weight acts on one end portion of the carriage while both end portions of the carriage are pulled in the sub-scan direction by means of the wire cables. As a result, the frame of the carriage vibrates. If the frame vibrates, the first mirror disposed on the carrier vibrates accordingly, and a resultant image is adversely affected.
On the other hand, it is known that a leak current occurs from a high-voltage-side harness of the cold-cathode fluorescent lamp. Thus, if the inverter circuit board is disposed at a middle portion of the carriage, as in the prior art, the high-voltage-side harness extends up to the middle portion of the first carriage, and the amount of leak current increases. If the leak current increases, the amount of light of the lamp decreases and the quality of an obtained image deteriorates.
In order to solve this problem, there is an idea that an insulating material is wrapped around the surface of the high-voltage-side harness, with a view to preventing leak current from the high-voltage-side harness of the cold-cathode fluorescent lamp. However, if the insulating material is wrapped around the harness, the cost of material increases, giving rise to a further problem.